Aluminium 'firsts' for Valhall heli hangar

Dutch specialist Bayards Aluminium Constructions added another impressive achievement to its catalogue of offshore industry credits last year when the industry’s first aluminium heli hangar left the company’s Heijningen yard production hall. OE looks back over how this highly complex job was done.

UK-based SLP Engineering, one of the EPC contractors handling the newbuild facilities for BP Norge’s Valhall Re-development project, entrusted Bayards with the engineering and construction of the 20m long, 17m wide and 9m high heli hanger for Valhall’s new integrated production and accommodation platform.

‘A super-shiny masterpiece, with welds as straight as an arrow and as flat as a mirror’, is how Bayards commercial director Dick de Kluijver describes the heli hanger, pointing out that this job saw the first time use by Bayards of friction stir welding (FSW) in an offshore application. ‘With the successful round-off of this highly complex project, and thanks to a combination of specialist engineering, professional project management and top quality welding, Bayards has considerably reinforced its leading position on the international rank list of engineering, design and fabrication companies of aluminium structures for the offshore industry,’ he adds. ‘A team of 30 experts was involved in the engineering and fabrication of the unique hangar during 20,000 manhours.’

Formidable challenges
Among the challenges on the Valhall heli hangar project was the complexity of the actual design. The project represented a first for all parties involved and therefore the design was a so-called ‘lifely’ document, with a number of adaptations having to made during the engineering phase.

‘I don’t hesitate to say that this has been the most complex engineering task we have ever carried out,’ notes Bayards projects manager Rolf van Opstal. ‘The only thing we got from the start was a layout drawing, with outline dimensions, support points and load stresses, from the architect. Nobody knew exactly how the hangar would look in the end, not even the SLP people, who, for their part, were depending on adaptations made by the main engineering company, Mustang, in Houston,’ he adds.

‘Each evolution on the total platform resulted in a snowball impact, and therefore also influenced the design of the heli hangar. Each time our engineers had to anticipate, of course in close cooperation with SLP.’

Van Opstal rates the application of the noiseless FSW method as the project’s most formidable challenge from a production point of view. He explains: ‘The maximum length of welding is 16m, and by welding many profiles together one can produce panels up to 20m in width. The profile thickness varies from 2mm to 12mm, at certified welding speeds up to 3.6m/min. The surface of the resulting panels is smooth, and requires no further grinding or brushing to improve the finish. The lower heat required for welding the profiles means that there is less distortion, and the technology produces panels with better mechanical properties than fusion welded.

‘The technique utilises frictional heating combined with forging pressure to produce high-strength bonds virtually free of defects. Friction stir welding transforms the aluminium from a solid state into a “plastic-like” state, and then mechanically stirs the materials together under pressure to form a welded joint. Another major advantage is that, by avoiding the creation of a molten pool which shrinks significantly on resolidification, the distortion after welding and the residual stresses are low.’

Once loaded out from Heijningen, the heli hangar, provided with four aluminium brace connections, was transported to the SLP yard in Lowestoft for installation on top of Valhall’s new living quarters.

The maximum strength on one support point is 130t.

Stair towers
Both SLP and the Valhall Re-development’s other EPC contractor Heerema Fabrication Group – whose Zwijndrecht yard is now adding the finishing touches to the new platform’s 11,000t main deck (OE March) – also tasked Bayards with producing other Norsok-certified aluminium items for the project.

Heerema ordered two stair towers 33.5m and 15m long respectively, with heat shield on both sides, as well a 15m long horizontal aluminium escape way. SLP required three complete aluminium stair towers, respectively 35m, 20m and 10m in length, including a number of internal aluminium steps for the extra modules.

Being approached by both SLP and Heerema at an early stage of the project helped contribute to the work’s successful execution, says Dick de Kluijver. ‘They made it possible for Bayards to use our knowledge optimally. They indicated their requirements and as an aluminium specialist we integrated our expertise and our engineering capacity in the total project.’

De Kluijver is in no doubt that aluminium will continue to gain in popularity in this sector because its ‘oustanding features – low weight, low life cycle cost, environmentally friendly, corrosion resistant, maintenance free – are becoming more and more important in offshore applications nowadays’. And he stresses that the weight saving on Valhall was considerable. ‘In total 200t of aluminium was needed to complete all the work,’ he points out. ‘The net delivered weight of the heli hangar amounted to almost 100t. Had steel been used, then certainly the hangar would have been noticeably heavier.’ OE

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